Thought I’d chime in too, my NExT which is in the same spot as yours had a similar thing after install.
No issues with feeling cold, but I did get some very slight tingling, and it got a bit itchy from time to time.
It subsided within a week or two (maybe 3 at the latest, memory is foggy).
I wouldn’t worry, something has been injected into your hand. It needs time to “cope” 
Just lay back, and enjoy the rest of your healing time.